The invention relates to an array of memory cells including diodes to select one of the memory cells and a corresponding method for forming the array.
In resistively switching memory cells, for example, phase change random access memory (PCRAM), the information is stored in a volume of switching active material, wherein the switching active material may switch between two states. In a first state the switching active material may have a high resistance, i.e. a low conductivity, and a lesser resistance, i.e. a higher conductivity, in a second state. Accordingly, the information of a bit may be assigned to a PCRAM cell, wherein the state of the cell reflects the status of the bit. Although the invention is described for PCRAM cells in the following the structure and methods can be used for any random access memory including diodes as selection means.
For reading a resistively switching memory cell the resistance of the volume of resistively switching material is sensed, i.e. the conductivity is sensed. This can be achieved, for example, by applying a predefined voltage to the cell and sensing the amplitude of the current flowing through the cell. For switching the state of a resistively switching memory cell a high current is sent through the volume of switching active material in order to heat and subsequently change the material from a one state to the other. Accordingly a selection diode comprised in the cell should be able to send a strong current through the cell.
An ever-challenging problem in the technology of memory is to reduce the size of a memory cell for increasing the density of memory cells, wherein at the same time an access device for selecting one cell must enable a high current through the cell.